UPDATE 11:30 AM: A short update to say, well, not much has changed. NWS-Blacksburg is estimating 3 p.m. for rain to snow changeover in the Blacksburg area and 4 p.m. for Roanoke. That could vary an hour or two either way. Some wintry mix and snow reports are occurring on the northwest fringe of the moisture shield in West Virginia into the far southwest corner of Virginia. The Radar / Future Cast link at right on this blog will give you an approximate idea where the mix (pink) and snow (blue) are being reported. END UPDATE
Summary: All indications are that the region is on track for 4+ inches of wet snow beginning early to mid-afternoon and continuing into the evening. Snow will be heavy at times with reduced visibilities and rapid collection of slushy accumulation on some road surfaces near rush hour. It should be over by 10 p.m.
It’s snowing this morning – in Jackson, Mississippi. And so begins a slow, sloshing trudge from a not-all-that-cold rain this morning in Southwest Virginia (temperatures in the 40s, mostly) to a potential heavy, wet snow event by late afternoon and early evening. The cold pocket aloft with the upper-level low spinning over Mississippi will slide northeastward, and a surface low forming just east of Atlanta will begin pulling cold air southward as the day progresses. We’ll likely see the rain/snow line begin to slip southeastward through West Virginia by mid to late morning as snow reports also begin to increase in central/eastern Tennessee and into some of Kentucky and eventually far southwest Virginia with the advancing upper low. During the afternoon, say between 1 and 4 p.m., temperatures are expected to be cooled in the low and mid levels of the atmosphere enough over Southwest Virginia east of I-77 (may happen before then to the west) that snow will begin reaching the ridgetops first, then progressively lower, with air temperatures also decreasing to near or barely above the freezing mark. If you’re anxiously waiting on snow this morning, this process will be like watching paint dry. Snowfall amounts by all available guidance appear to be on track for widespread 4+ inches across the region, with some amounts up to 12 inches, or maybe a little more, especially in higher elevations along the I-81 corridor southwest of Roanoke and westward. The snow won’t last long, probably no more than 5 to 8 hours at any location, but will likely come down fast and furiously at times, with some low visibilities developing near rush hour. It’s that intensity that is expected to overcome a relatively mild, moist ground, collecting on grass and exposed objects first, then forming a slushy layer on the ground once the rate of snowfall exceeds the melt rate. Once the thin layer of slush develops, snow can collect on top rapidly. In the heaviest periods of snow, roads may become slushy and even ice/snow covered — I-81 southwest of Roanoke is a particular concern, with its steep hills and curves, and considering the trouble that ensued there from heavy snowfall rates in December 2009. Due to the heavy, wet nature of the snowfall, especially in its early stages, there may be some tree and power line damage, similar to what we saw last Feb. 19. This snow will probably be moving east of us by 10 p.m., and a cold night with lows in the upper teens and 20s will ensue that will freeze slush and water on streets.